The modulation of murine thymocyte surface receptors for the 71,000 dalton major envelope glycoprotein, gp71, of Rauscher murine leukemia virus has been examined utilizing a highly specific (125I) radiolabeled gp71 binding assay. Cell surface receptors for ecotropic murine leukemia virus respond similarly to ligand-induced topographical modulation as do other cell surface receptors indicating that their anchorage and movement in the cell membrane is mediated via microfilament and microtubule cytoskeletal structures. A reduction in the affinity constant, Ka, and number of available receptor sites on thymocytes for gp71 by adenosine triphosphate has been demonstrated. This effect is specific in that no modulation is seen with the other ribonucleotides, deoxynucleotides or cAMP, ADP or AMP. The inclusion of an ATP generating system in the receptor assay reduced the amount of ATP needed to reduce gp71 binding. Non-hydrolyzable analogs of ATP, i.e. App(NH)p, also modulated receptor activity suggesting an allosteric interaction of ATP with the gp71 receptor complex.